1. Field of the Invention
This invention relates to a discharge chamber incorporated in a plasma addressed display device or a like device and a method of manufacturing the same, and more particularly to an electrode structure of a discharge chamber having a linear discharge channel and a method of forming the electrode structure.
2. Description of the Related Art
A plasma addressed display device in which a discharge chamber having a linear discharge channel is incorporated is already known and disclosed, for example, in Japanese Patent Laid-Open Application No. Heisei 4-265931, which corresponds to U.S. patent application Ser. No. 07/837,971 filed on Feb. 20, 1992 and assigned to the assignee of the present patent application. In order to clearly show the background of the invention, an outline of the structure of a conventional plasma addressed display device is described with reference to FIG. 5. The plasma addressed display device shown has a structure wherein a display chamber 51, a discharge chamber 52 and an intermediate substrate 53 are layered with each other with the intermediate substrate 53 interposed between the display chamber 51 and the discharge chamber 52. The display chamber 51 is constructed using an upper side glass substrate 54 and has a plurality of signal electrodes D formed in parallel to each other in the direction of a column of a matrix on an inner major surface thereof. The glass substrate 54 is adhered to the intermediate substrate 53 with a predetermined gap left therebetween by means of a spacer 55. A liquid crystal layer 56 is filled in the gap. Meanwhile, the discharge chamber 52 is constructed using a lower side glass substrate 57. A plurality of plasma electrodes 58 are formed on an inner side major surface of the substrate 57 such that they extend in the direction of a row of the matrix perpendicularly to the signal electrodes D. The plasma electrodes 58 alternately functions as an anode A and a cathode K. A plurality of barrier ribs 59 are formed on and along the plasma electrodes 58. The barrier ribs 59 contact at the top ends thereof with the intermediate substrate 53 and serve as a spacer. The lower side glass substrate 57 is adhered to the intermediate substrate 53 by means of a seal member 60. An airtight enclosed space is defined between the lower side glass substrate 57 and the intermediate substrate 53. The space is partitioned by the striped barrier ribs 59 to construct discharge channels 61 which individually make row scanning units. Ionizable gas is enclosed in the individual discharge channels 61.
FIG. 6 schematically shows an electrode structure of a conventional discharge chamber. A plurality of electrodes 102 patterned in stripes are formed on a surface of a substrate 101. The striped electrodes 102 are arranged in a spaced relationship by a pitch P and individually have a width dimension W1. A barrier rib 103 is formed on each of the striped electrodes 102. Also the striped barrier ribs 103 are arranged in a spaced relationship by the same pitch P and individually have a width dimension W2 which is set smaller than the width dimension W1 of the striped electrodes 102.
A subject to be solved by the invention will be described with reference to FIG. 7 which shows the striped electrodes 102 and the striped barrier ribs 103 formed by different pitches from each other with respect to the condition shown in FIG. 6. Such a striped pattern as shown in FIG. 7 is formed generally using a mask. Although the electrodes 102 and the barrier ribs 103 originally have an equal pattern arrangement pitch P, they have different width dimensions W1 and W2 from each other. Accordingly, the mask employed for formation of the electrodes 102 and the mask employed for formation of the barrier ribs 103 are conventionally different from each other. In this instance, in order to align the electrodes 102 and the barrier ribs 103 with each other, the two masks for them have an equal striped pattern pitch and are aligned accurately with each other.
For formation of electrodes or barrier ribs, a thick film printing procedure using a screen mask is employed usually. The screen mask includes a frame on which a screen mesh is stretched under tension. Photolithography is applied to a screen mesh to which a photosensitive agent is applied to form a predetermined mask pattern. However, since the screen mesh is stretched under tension, it is difficult to set the pitches of striped patterns to a completely equal value between different screen masks, and actually, a fixed pitch error .DELTA.P is involved between the two pitches P. In addition, when thick film printing is performed, a pressure is applied to the screen mask by a squeegee to deform the screen mask. The degree of such deformation is delicately different between individual screen masks, and the pitch of a striped pattern actually printed is deviated from an aimed value. Consequently, it is actually difficult to align the lower layer electrodes 102 and the upper layer barrier ribs 103 actually with each other, and there is a subject to be solved in that a pitch error is resulted from the difficulty.
If there is some relative positional displacement between the electrodes and the barrier ribs, then the problem arises that operation of the discharge chambers becomes unstable. This will be described briefly specifying detailed dimensions with reference to FIGS. 8(A) and 8(B). In particular, FIG. 8(A) shows electrodes and barrier ribs which have no relative positional displacement from each other. A plurality of plasma electrodes 151 alternately function as an anode A and a cathode K and are arranged by the pitch of, for example, 410 .mu.m on a substrate 152. A barrier rib 153 is formed in an overlapping relationship with and on each of the plasma electrodes 151. The width dimension of the barrier ribs 153 is set to 120 .mu.m, and the width dimension of the plasma electrodes 151 is set to 300 .mu.m. A linear discharge channel 154 is formed between each adjacent ones of the barrier ribs 153, and an anode A and an adjacent cathode K are partially exposed in the inside of the linear discharge channel 154. Plasma discharge is produced by application of a predetermined voltage between the anode A and the cathode K. In order to stably maintain the plasma discharge, a fixed electrode exposed area must necessarily be assured. Particularly the exposed area of the cathode K is dominant, and the exposed electrode width of at least 60 .mu.m must necessarily be assured. In this instance, if it is assumed that the positioning error between the barrier ribs 153 and the electrodes 151 is approximately .+-.30 .mu.m to the utmost, the exposed electrode width of at least 90 .mu.m must necessarily be assured on the opposite sides of each barrier rib 153 as seen from FIG. 8(A). Consequently, in the arrangement shown in FIG. 8(A), the width of the electrodes is set to 300 .mu.m and the width of the barrier ribs is set to 120 .mu.m. As a result, only an opening width of 110 .mu.m can be taken between each adjacent anode A and cathode K, which results in sacrifice of the contrast as considered as a display device. Further, FIG. 8(B) shows electrodes and barrier ribs between which positional displacement of 30 .mu.m is exhibited. In this instance, in a discharge channel 155, the exposure width of the cathode K is 60 .mu.m which is a minimum required value. Should positioning displacement of a larger dimension occur, the plasma discharge in the discharge channel 155 will be very unstable. On the other hand, in an adjacent discharge channel 154, the exposure width of the cathode K increases up to 120 .mu.m, and consequently, stabilized discharge is obtained. In this manner, with the conventional structure described above, if positioning displacement occurs between the barrier ribs and the electrodes, then the discharge channels alternately present different intensities of plasma, and consequently, there is a subject to be solved in that the picture quality is deteriorated by such alternate different intensities of plasma as considered as the entire display device.